Potentiometer



Nov. 1 0, 1959 DE wm" T. VAN ALEN 2,912,663

POTENTIOMETER Filed Feb. 7, 1957 Zr 1 m INVENTOR. DE W/rr 7'. 1 0 ,QLs/ BY W. Wu ALA.

A I'TORNEV United States Patent POTENTIOMETER De Witt T. Van Alen, Delavan, Wis., assignor to The George W. Borg Corporation, Chicago, 11]., a corporation of Delaware Application February 7, 1957, Serial No. 638,861

4 Claims. (Cl. 338-170) This invention relates to improvements in potentiometers.

In the specific embodiment disclosed herein, a single turn rotary potentiometer has a contact slider mounted for rotation on a circular path and a resistance element wound on a helical path. This construction diifers markedly from prior art single turn potentiometers known to me in which it is conventional to wind the electrical resistance element on a circular path having an arcuate extent less than 360. To preclude short circuiting the ends of such windings, prior art resistance windings are circumferentially spaced at their terminal portions. Accordingly, as the rotating contact element passes over the gap thus provided, it will momentarily lose the support which the winding otherwise provided and will be required to jump the gap.

The usual contact biasing pressure to which the contact slider is subject will project the contact radially outwardly in the area of the gap and the contact will collide under considerable impact shock against the terminal end of the resistance element at the end of the gap. Accordingly, both the contact slider member and the terminal portion of the resistance element are subject to considerable wear. Prior art potentiometers having continuously rotating contact members are particularly subject to wear and damage.

In the device of the present invention, the resistance element is wound on a path which is helical with respect to the circular path on which the contact slider is rotated and the terminal portions thereof overlap axially. The contact slider is of sufficient width to bridge across the overlapped terminal portions of the helically wound resistance .element so that the contact is constantly supported on a uniform radius, even in passing from one terminal portion of the winding to the other. Accordingly, there is no gap to traverse, the slider element is not required to jump from one end of the winding to another in traversing any gap and the transfer of the slider from one terminal portion of the resistance element to the other is made smoothly and completely without shock.

Moreover, wear is distributed over substantially the entire width of the contact element by reason of the constant shifting of the point of contact between the resistance element and the contact element as the slider traverses a circular path with respect to which the winding is helically disposed. In addition, unlike prior art devices aforesaid, the pressure of the instant control slider against the winding is uniform throughout its circular traverse.

The contact slider per se is unique in the device of the present invention. Unlike prior art devices in which the slider provides its own spring pressure against the resistance element, the contact slider of the present invention is made rigid but is extremely light weight and of low mass and inertia for high compliance with the re sistance element. Contact pressure is provided for by a separate spring which biases the contact toward the winding under relatively constant pressure. The spring is desirably of the multi-turn helical type.

In the drawing:

Fig. 1 is an axial cross section taken through a single turn potentiometer embodying the present invention.

Fig. 2 is a fragmentary view partly in cross section and partly in elevation taken through the device of Fig. 1 and substantially along the line 22 thereof.

Fig. 3 is a fragmentary perspective view illustrating a helically wound resistance element in operative association with the contact portion of the slider.

Fig. 4 is a plan view of the device of Fig. 3, the view being somewhat enlarged to illustrate details of construction.

Fig. 5 is a fragmentary perspective view of the contact slider portion of the device.

Reference may be made to my Patent 2,665,355 which shows a ten turn potentiometer with a helically wound resistance element. The device of the present invention may have a similar resistance element which is limited, however, to a single active turn. The resistance element desirably has an insulated core of soft copper wire and a helical winding of bare resistance wire wound on the core in spaced turns. The resistance element 10 may be molded into the inner surface of a dielectric body shell 11 which has end disks 12 and 13 fastened thereto by means of the channel-shaped clamping bands 14. The disks 12, 13 are each provided with ball bearings 15 for the rotatable support of a shaft 16 on which the arm 17 of a contact slider is mounted as is hereinafter explained more in detail.

The contact slider 17 is electrically connected to a slip ring 18 which has a groove 19 to receive the hair pin type wire rod brush arms 20. The brush arms 20 are mutually connected to a terminal post 23 to which external electrical connection may be made.

. The helical winding 10 has axially overlapping terminal portions 28 best shown in Figs. 3 and 4. Electrical terminal connections are made to the winding by means of the lead wires 24, 25 which are soldered to the winding and are connected to the terminal posts 26, 27 shown in Fig. 2. The terminal wires 24, 25 are desirably soldered to the winding 10 with a minimum arcuate spacing so that almost the full arcuate extent of the helical winding is active. The arcuate extent or" the active winding between the terminal wire 24, 25 is desirably in the range of about 350 to 355 or more. To preclude the contact slider element from bridging over and short circuiting the resistance element between the terminals 24, 25 through the inactive portions 28 of the winding, the resistance wires of such inactive portions 28 are severed as close as possible to wires 24, 25, as is diagrammatically indicated at 29. While the winding portions in the short arc between wires 24, 25 are electrically inactive, they nevertheless bodily support the contact slider as it passes from one terminal of the active winding to the other terminal thereof.

The ends of the inactive terminal portions 23 of the Winding may be soldered as at 30 to preclude fraying and unwinding of the resistance wires thereof.

The novel contact slider of the present invention is best shown in Fig. 5 and consists of a channel-shaped relatively rigid arm member 17 of extremely light gauge and hence of light weight and low mass and inertia. In practice I prefer to use for its electrical contact properties a metal by the trade name Paliney No. 7 which is a proprietory product of the J. M. Ney Company and is an alloy consisting of 10% gold, 10% platinum,, 35% palladium, 30% silver and 15% copper. The gauge of the metal from which the contact is stamped is very thin, desirably about .0035 inch. A central medial slot 33 is left in the web portion 34 of the contact to further lighten and reduce the mass and inertia of the contact.

The channel flanges 35 of the contact arm are provided the arm is journaled for rotation about the pintle 37. The pintle is mounted in the cars 38 fastened to asupport block 39 which is in turn mounted on the dielectric hub 4.9 which also carries the. slip ring 13.

Electrical connection is made between theslip ring 18 and the contact slider arm 17 through a helically wound multi-turn conductive spring 43 which may be coiled about the pintle 3'7 and biases. the contact slider 17 toward engagement with the resistance element 10. The extreme lightweight and low mass and inertia of the contact carrier 17 render it highly compliant and quickly responsive to any irregularities in the surface of the electrical resistance element 16*. This feature, together with the axially overlapping terminal portions of the helical winding 1% provide for continuous engagement of the contact with portions of the winding and the contact slider is not subject to jumping. wear is manifested on the bearing surfaces of the respective parts and the operation of the device is mechanically smooth. By distributing the wear over the entire surface of the contact slider, its life is additionally prolonged and even in continuous rotating service the parts will last almost indefinitely. The multi-turn helically wound spring 43 supplies substantially constant biasing pressure I through a substantial range of oscillatory movement of the arm 17 about pivot 37. Accordingly, the need for adjustment of the contact in the course of its assembly into the potcntiometerlis virtually eliminated.

I claim: 7

1. A single turn potentiometer having a helical Winding with axially overlapping terminal portions, a contact slider and means mounting the contact slider for rotation on a circular path, said slider having a contact portion of sufiicient width to span across and contact both terminal portions of the winding at the overlap thereof whereby Accordingly, very little" 4 support for the slider is transferred from one terminal portion to the other without change in support radius as the slider traverses said overlapped terminal portions.

2. The device of claim 1 in combination with terminal leads connected to the terminal portions of said winding, the points of connection of said leads in said winding being arcuately spaced by less than 360 to define an active portion of said winding, the remainder of said winding being inactive, said inactive remainder of said winding mechanically bridging between said points of connection but being severed beyond said points of connection to electrically isolate the points of connection except through the active portion .of said winding.

3. The device of claim 1 in combination with a rotor having a mounting radially without said winding for said contact slider, said mounting comprising a pintle and said slider comprising a lever arm pivotally mounted on the pintle, and spring means biasing said arm radially outwardly about said pintle and toward engagement with said winding. 7

4. The device of claim 3 in which said lever arm comprises a substantially rigid channel member and said spring means comprises a multi turn coil helically wound about the pintle on which the arm pivots.

References Cited in the file of this patent UNITED STATES PATENTS Suchanek July 3, 1917 

